Emission microscopy is a rapidly evolving tool for detecting and characterizing certain defects or potential defects in semiconductor integrated circuits, wherein such defects or potential defects emit low levels of light when the integrated circuit is subjected to electrical activating signals. Faint radiation can be emitted from portions of electrically activated semiconductor integrated circuits by a number of fundamental mechanisms, such as, for example, by avalanche luminescence, by dielectric luminescence, and by so-called forward bias emission. Additionally, emission microscopy can provide a high resolution detection of high temperature regions or domains within a semiconductor integrated circuit.
An emission microscope is an optical microscope customized to provide particular features required to detect luminescence as well as to view a semiconductor integrated circuit under visible light conditions, so that defects generating light emission can be correlated with the physical and electrical layout of the integrated circuit. An emission microscope may include a higher magnification analytical probe station for microprobing certain sub-regions or domains of the integrated circuit, and alternatively, for selectively ablating material from certain domains of the integrated circuit or for conducting micro repair of certain domains. Other features of an emission microscope may be a high resolution and high sensitivity image capture system, image data storage means, image data processing means, and an image display system.
In order to provide "global" characterization of light emission of a semiconductor integrated circuit, the macrolens system of an emission microscope should provide at least the following features: (i) a high light transmission value through the lens system; (ii) a wide field of view of an object to be characterized, the field of view preferably covering all or at least a substantial portion of the area of the semiconductor integrated circuit object positioned in the object plane of the macrolens system; (iii) a spectral range of light transmitted through the macrolens system which includes visible light and radiation emitted by the integrated circuit under test; and (iv) sufficient spatial resolution (described as a modulation transfer function) of the macrolens system to detect desired details of the integrated circuit under test.
With respect to the light transmission value of a lens system, the amount of light transmitted through a lens is proportional to (NAO).sup.2 /(MAG).sup.2, where NAO is the numerical aperture of the object and MAG is the overall magnification of the lens system. A macrolens system optimized to provide both a high light transmission value and a wide field of view at the object plane thereof has not been available heretofore, since these two features of a macrolens system cannot be readily obtained by simply combining two or more commercially available lens assemblies, such as, for example, two camera lens assemblies or two slide projector lens assemblies. For example, U.S. Pat. No. 4,680,635 to Khurana discloses in col. 3, lines 37-53 a microscope optics system utilizing two lenses (16 and 17) wherein a primary lens 16 has a high numerical aperture and a high magnification, and a secondary lens 17 is used to reduce the overall magnification of an image. That system, however, provides a substantially reduced field of view at the object plane, thereby necessitating multiple adjacent sub-areas to be imaged and characterized so as to generate a composite image comprising all or a substantial portion of the area of a semiconductor integrated circuit under test.
In U.S. Pat. No. 4,755,874 to Esrig et al, there is disclosed in FIG. 3 thereof a macro optic system 30 comprising back-to-back photo lenses which in combination provide a numerical aperture of at least 0.025 at an overall magnification of 1X (col. 2, line 68; col. 3, lines 64-65). While Esrig et al mention that the numerical aperture of the macro optic system 30 preferably is in the range from 0.17-0.34 or higher (col. 3, line 66), these authors also point out (col. 2, lines 10-13) that the requirement of a high numerical aperture and low magnification has not previously been available in lenses having sufficient quality. Moreover, Esrig et al do not suggest a design or configuration of a macro optic system which might even conceptually approach the numerical aperture range from "0.17-0.34 or higher."
It is apparent from a detailed review of the foregoing publications that a macrolens system for emission microscopy which combines the desirable features of a high numerical optical aperture and low overall magnification with a wide field of view have been desired for some time but not been available as an optimized macrolens system.
Accordingly, it is desirable to provide an optimized macrolens system having these and other features suitable for incorporation into an emission microscope in which a number of auxiliary optical components can be provided as well.